One vertex per element, one color per generator, with an edge from x to x·s.
(1,2,5,7)(3,4,8,6)(9,10,11,17,13,18,14,15)(12,20,22,16,21,23,19,24)(25,26,29,31)(27,30,35,38)(28,32,36,40)(33,37,34,39)(1,3,5,8)(2,6,7,4)(9,11,13,14)(10,15,18,17)(12,19,21,22)(16,23,24,20)(25,27,29,35)(26,30,31,38)(28,33,36,34)(32,37,40,39)(9,12,13,21)(10,16,18,24)(11,19,14,22)(15,23,17,20)(27,33)(28,36)(30,37)(32,40)(34,35)(38,39)(1,4,5,6)(2,3,7,8)(10,17)(11,14)(15,18)(16,20)(19,22)(23,24)(26,31)(30,38)(32,40)(37,39)A Cayley diagram is a choice, not a fact about the group. Another drawing of this group — in a book, or on a different generating set — may look nothing like this one.